Direct pyrolysis of non-condensed gas oil fraction



Dec. 30, 1969 -J. NEWMAN ETAL 3,487,006

DIRECT PYROLYSIS OF NON-CONDENSED GAS OIL FRACTION Filed March 21, 1968 Steam Gas Oil Goker Tower Gus 5 Nophtho 57 Petrochemlcol Products 52 1/ I I4 ,0 Nuphthl superheated A Steam Gas Oil Tower S-teom Petrochemical 3/ CokerHeater Products INVENTORS Juhon Newman John Cospers ATTORNEYS v Pyrol'ysis 55' I v Coker United States Patent U.S. Cl. 208-93 8 Claims ABSTRACT OF THE DISCLOSURE A process for integrating crude fractionation facilities with the production of petrochemical products wherein light distillates are initially separated from a virgin crude in a first fractionator. The light distillate free crude is mixed with steam and passed through the convection section of a pyrolysis heater and introduced into a gas oil tower. The gas oil overhead from the gas-oil tower is introduced, without condensation, into the radiant heating section of the pyrolysis heater to effect cracking thereof to desired petrochemical products. The residuum from the gas-oil tower may be further treated; e.g., by coking, to produce lighter products.

This invention relates to petroleum processing and more particularly to a process for effectively integrating crude fractionation facilities with petrochemical facilities for the production of petrochemicals and petroleum products.

In the petroleum industry, a crude oil is first subjected to a series of fractionations to recover various feed stocks for the production of petroleum products. Thus, for example, a crude oil is heated and introduced into an atmospheric fractionation tower wherein light distillates, including naphtha are separated from the crude. The crude, now free of light distillates, is passed through a heater and introduced into a vacuum flash tower wherein gas oil is recovered from the crude. The recovered gas oil is condensed, cooled and then transported to pyrolysis facilities to produce desired petrochemical products, such as ethylene, propylene, butadiene and the like. The pyrolysis process is effected in the vapor phase and, consequently, the gas oil must be revaporized, resulting in redundant processing which increases overall cost. In addition, the vaporization of the gas oil in the convection section of a pyrolysis heater produces coking problems associated with effecting 100% vaporization of the gas oil.

Accordingly, an object of this invention is to provide an improved process for producing petrochemical products.

Another object of this invention is to provide a process for lowering the overall cost of producing petrochemical products.

A further object of this invention is to provide a process which eliminates the redundant processing steps employed in producing petrochemical products from a crude oil.

Yet another object of this invention is to provide a process wherein petrochemical production is efiectively integrated with crude oil processing.

These and other objects of the invention should be readily apparent from the following description of the invention when read with reference to the accompanying drawing wherein:

FIGURE 1 is a simplified schematic flow diagram of an embodiment of the invention; and

FIGURE 2 is a simplified schematic flow diagram of another embodiment of the invention.

3,487,006 Patented Dec. 30, 1969 ice The objects of this invention are broadly accomplished by introducing a crude oil into a first fractionator wherein light distillates, including naphtha, are separated from the crude. The crude, now free of light distillates, is diluted with steam, passed through the convection section of a pyrolysis heater and introduced into a gas oil tower. The overhead from the gas oil tower, primarily containing gas oil, is introduced without condensation thereof, into the radiant heating section of the pyrolysis heater wherein the gas oil is pyrolyzed to desired petrochemical products.

The invention will now be described in more detail with reference to the accompanying drawing wherein valves, pumps, etc. have been omitted to facilitate the description thereof. The placing of such equipment and various other equipments are deemed to be within the scope of those skilled in the art.

Referring now to FIGURE 1, crude oil in line 10 is passed through crude heater 11 wherein the temperature of the crude is raised to between about 200 and about 700 F. The heated crude from the heater 11 in line 12 is introduced into a fractionator 13, containing suitable gas liquid contacting devices 14, and operating at a pressure falling within the range between about 15 and about p.s.i.g., an overhead temperature falling within the range between about 200 and about 500 F., and a bottoms temperature falling within the range about 400 and about 700 F., in order to separate light distillates; e.g., naphtha, from the crude.

An overhead, containing light distillates including naphtha, is withdrawn from fractionator 13 through line 15 and passed to further processing (not shown). Thus, for example, the naphtha in the overhead from the fractionator 13 may be recovered as either liquid or vapor for passage to naphtha pyrolysis coils.

A bottom, containing the light distillate free crude oil, is withdrawn from fractionator 13 through line 16, mixed with dilution steam in line 17, and the combined stream in line 18 passed through the convection section 19 of a pyrolysis heater 21 wherein the temperature thereof is raised to between about 600 and about 900 F. The dilution steam added to the crude oil in line 16 is generally added in an amount to provide between about 0.1 and about 1.5 lb. of steam per 1b. of crude. The heated mixture from the convection section 19 in line 22 is introduced into a fractionator 23, containing suitable gasliquid contacting devices 24, and operating at a pressure falling within the range between about 15 and about 200 p.s.i.g., an overhead temperature falling within the range between about 500 and about 700 F. and a bottoms temperature falling within the range between about 600 and about 850 F., to separate gas oil from the crude. The fractionator 23 is provided with a reflux condenser 25 to supply the cooling requirements and a steam line 26 to provide steam stripping of additional gas oil from the crude residuum.

An overhead, containing the gas oil, generally a fraction having upper and lower cut points falling within the range between about 200 and about 1000 F., is withdrawn from fractionator 23 through line 27, admixed with superheated steam in line 24 to prevent condensation thereof and passed through tubes in the radiant heating section 29 of the pyrolysis heater 21 wherein the gas oil is cracked to desired petrochemical products, such as ethylene, propylene, etc. The pyrolysis furnace is of a type known in the art and is operated under conventional conditions; e.g., outlet temperatures falling within the range between about 1350 and about 1650 F., pressures falling within the range between about 0 and about 50 p.s.i.g., and preferably residence times of less than about 1 second.

A residuum, is withdrawn from fractionator 23 through line 31, and may be passed to further processing. Thus,

3 as shown in FIGURE 1, the residuum in line 31 is admixed with steam in line 32, passed through a coker heater 33 and introduced into coke drums 34. The coker heater 33 and coke drums 34 are operated under conditions, known in the art; e.g., a temperature of about 900 to about 1000 F. and a pressure between about and about 70 p.s.i.g., to produce coke and crude vapors. Synthetic crude vapors are withdrawn from the coke drums 34 through line 35 and introduced into the fractionator 13 to recover the various components therefrom. In this manner, residuum processing is effectively integrated with the processing of virgin crude with the fractionators 13 and 23 functioning both as fractionators for recovering the components of virgin crude and as the coker combination fractionator generally employed in a coking process.

Alternatively, as shown in FIGURE 2 wherein like numerals designate like parts, the residuum from fractionator 23 in line 51 may be introduced into the coker combination tower 52 of a conventional coking unit. The bottoms from the tower 52 is passed through a coking heater 53 and introduced into coke drums 54, operating under the conditions generally known in the art. Synthetic crude vapors are withdrawn from the coke drums 54 and introduced into the combination tower 52 to recover the various fractions. The coker gas oil fraction is withdrawn from tower 52 through line 55 and passed to the convection section 19 of the pyrolysis heater 21 through line 57 along with steam introduced through line 17 and alternatively to the gas oil tower 23, as reflux through line 58. The remaining fractions, containing naphtha are withdrawn from tower 52 through line 56 and passed to further processing (not shown) or alternatively introduced as reflux in the upper section of naphtha tower 13 with subsequent passage to naphtha pyrolysis coils along with virgin naphtha in either liquid or vapor form.

The invention is further illustrated by the following example but the scope of the invention is not to be limited thereby.

EXAMPLE A crude oil is treated under the conditions listed in the following table.

TABLE Temp., F. Pressure, p.s.i.a. Flow rate, lbs/hr.

The gas oil recovered from the gas oil tower 23 boils in the range between 350 and 850 F.

The pyrolysis heater 21 is operated at an outlet temperature of 1500 F., a pressure of psig and a residence time of 0.5 second.

The process of the invention has numerous advantages over those heretofore employed in the art. The passing of gas oil vapor directly to the pyrolysis furnace avoids the coking problems associated with accomplishing vaporization of the gas oil in the convection section of the pyrolysis heater. Thus, gas oil fractions having a boiling point higher than those conventionally used may be employed in the process of the invention. In addition, the elimination of the conventional practice of condensing and revaporizing gas oil for the pyrolysis heaters, results in savings in utilities, processing equipment and tankage. furthermore, by introducing steam into the bottoms from the naphtha flash tower, upstream of the convection section, the gas oil is vaporized at lower temperatures, such lower temperatures being below those at which residuum cracking and coking is initiated. Since steam is required in the subsequent pyrolysis process, the effect of a partial vacuum is obtained without conventional vacuum tower equipment and without increasing steam consumption.

Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A process for integrating crude oil fractionation with the production of petrochemical products comprising:

(a) introducing crude oil into a first fractionation zone wherein light distillates are separated from the crude;

(b) withdrawing a light distillate free crude from the fractionation zone;

(0) adding steam to the heavy crude fraction from step (d) passing the mixture of step (c) through the convection zone of a pyrolysis heater to effect heating thereof;

(e) introducing the heated mixture from step (d) into a second fractionation zone to separate gas oil vapor; and

(f) introducing the gas oil vapor from step (e) into the radiant heating zone of the pyrolysis heater to effect pyrolysis thereof to petrochemical products.

2. The process defined by claim 1 wherein the mixture in step (d) is heated to a temperature between about 600 and about 900 F.

3. The process defined by claim 2 wherein the steam added in step (c) is between about 0.1 and about 1.5 lb. per lb. of crude.

4. The process as defined by claim 1 and further comprising: recovering residuum crude from step (e), introducing the residuum into a coking zone to effect coking thereof, and introducing the vapors recovered from the coking zone into the fractionation zone of step (a).

5. The process as defined by claim 1 and further comprising recovering residuum crude from step (e), introducing the residuum into a coking zone to effect coking thereof, recovering a gas oil fraction from the coking zone and passing the gas oil fraction from the coking zone to the second fractionation zone.

6. The process defined by claim 1 and further comprising adding superheated steam to the gas oil vapor from step (e) prior to step (f).

7. The process defined by claim 1 wherein the gas oil vapor has upper and lower cut points falling within the range between about 200 and about 1000 F.

8. The process defined by claim 1 wherein the second fractionation zone is operated at a pressure between about 15 and about 200 p.s.i.g.

References Cited UNITED STATES PATENTS 2,844,524 7/1958 Ernst 20894 2,852,441 9/1958 Martin et al. 208-94 2,868,717 1/1959 Claridge 208-94 3,234,118 2/1966 Chen 20893 3,437,584 4/1969 Hamblin 20893 HERBERT LEVINE, Primary Examiner US. Cl. X.'R. 

